Julian Assange sought political asylum because he believed he would not "see the light of day for 40 years" if he was extradited to Sweden, according to his New York-based lawyer.

Michael Ratner of the Center for Constitutional Rights, which represents the WikiLeaks founder in the US, said Assange and his legal team considered it highly likely that he would face an onward extradition to the US if he were sent to Sweden.

"The concrete reality [is] that he was facing a political prosecution in the US, he was facing the death penalty or certainly life in jail. Faced with that, he had extremely limited choices."

Barring a last-ditch appeal to the European court of human rights, Assange could have expected to be extradited imminently, after the supreme court rejected the last of his attempts to resist removal to Sweden over accusations of sex assaults made by two women in August 2010.

The Assange team believes the US is likely to seek to prosecute him on espionage charges, which carries a potential death penalty, and that his chances of resisting any such extradition warrant would be more difficult in Sweden, where he would not receive bail during investigations into the alleged sex crimes and where his lawyers believe political and public opposition to a US extradition claim would be weaker.

The US empanelled a secret grand jury investigation into WikiLeaks and Assange in May 2011, but has not issued any requests for his extradition to the UK or Sweden. However, Ratner said both he and Assange believed it was "more likely than not" that a sealed indictment had been drawn up.

Assange's legal adviser Jennifer Robinson said in February that she and Assange had discussed the possibility of his seeking political asylum. Ratner said he had had no warning of the plan, however.

Ecuador's foreign minister, Ricardo Patiño, said on Tuesday the Wikileaks founder had written to the country's president, Rafael Correa, to ask for asylum. Assange interviewed Correa last month for his TV show The World Tomorrow, broadcast on the Russian state-sponsored channel Russia Today.

It was during this interview that an offer of asylum was made, the Associated Press reported, quoting a woman who had been present during the interview but had spoken on condition of anonymity. It did not say whether the offer was personally made by Correa.

It is not at all clear what the Australian's next move can be, even if Ecuador does grant his request.

The Foreign Office has confirmed the embassy is diplomatic territory, and that while Assange remains there he is "beyond the reach of police". However, he will be subject to immediate arrest if he attempts to leave, the Metropolitan police have said, after confirming he had breached his bail conditions.

Assange's passport is understood to have been surrendered to British authorities, and even were he to be given a diplomatic passport, this would not confer automatic immunity, the British authorities indicated.

Anna Alban, the Ecuadorian ambassador, had a "cordial and constructive" meeting with Foreign Office officials on Wednesday morning to discuss the case, she said in a statement. "I welcome the statement from the UK government last night in which they stated that they (the UK government) would work with the Ecuadorian government to find a resolution.

"I also took the opportunity to explain that the decision on Mr Assange's application would be assessed by the department of foreign affairs in Quito and would take into account Ecuador's long and well-established tradition in supporting human rights.

She said it was not Ecuador's intention "to interfere with the processes of either the UK or Swedish governments", adding that she would make herself available to British government officials at any time "so that we can find a just and fair solution to this situation".